Tin recovery process



W. H. OSBORN TIN RECOVERY Pnocss Dec. 8, r1942.

Filed Feb. 7, 1941 ruban@ Patented Dec. 8, 1942 S PATENT OFFICE asomar TIN RECOVERY PROCESS William H. Osborn, New York, N. Y., assignor to Phelps Dodge Corporation, New York, N. Y., a corporation of New York Application February '1, 1941, serial No. 377,823

19 Claims.

This invention relates to the recovery of tin and more particularly to improvements in the procedures for the separation of tin from other metals commonly associated with it. In the decipally ofthe mineral cassiterite a tin oxide hav-` ing the formula SnOz), oxides of iron such as hematite or combined iron silicates, and silica such as the mineralquartz or combined silicates. v

In addition to these principal constituents, there are generally the minerals of other metals such as arsenic, antimony, lead, bismuth, silver, etc., present in relatively minor proportions. When such concentrates are melted down by application of temperature and in the presence of just sufficient reducing agents, for example, solid carbonaceous matter such as coal or coke, or gaseous reducing agents such as carbon monoxide or hydrogen, the tin is rst reduced to stannous oxide and combines with the silica to form a fluid stan- 5 nous silicate of the generalized formula (SnO) :(SiOzM, and the ferric oxides are reduced to ferrous oxide to form ferrous silicates of the generalized formula (FeO)I(SiO2)y. If reduction is carried further than thepoint at which these tin and iron silicates are formed, they will be reduced to metallic tin which will remain in equilibrium with the stannous silicates of the slag, and if carried far enough iron compounds will be reduced to metallic iron which Will remain in equilibrium with the ferrous silicates of the slag. These equilibriums are such that when the ratio of iron to tin in the original ore or concentrates is relatively high, and it is desired to reduce the amount of tin in the slags to a point where the slag may be discarded .without excessive loss of tin, it is necessary to reduce to metal, along with the tin, a certain proportion of the iron. The proportion of iron reduced with tin increases rapidly as the ratio of iron to tin in the original ore or concentrates increases.

If lime is added to the ore or concentrate 'to be smelted, it has the eiect of increasing the ratio between metallic tin and tin combined as a silicate so that lower commercial slags can be pro- A Previous methods of carrying out thissulfidation I or by reaction with carbon and sulfur duced by the addition of lime, but the proportion of iron reduced with the tin to metal remains roughly the same.

Ihus, in order to produce tin free or relatively free from iron in the reduction of 10W grade tin concentrates, it is necessary to limit the reduction to appoint where excessive amounts of tin will remain in the slag.

In order to meet this problem,`previous commercial practice in the smelting of tin ores has been to first reduce the ore by smelting with carbonaceous matter only to a point where metallic tin relatively free of iron is lseparated from the molten bath, leaving a slag which contains too much tin to allow its rejection. This slag is then generally separated from the reduced tin metal by skimming and further reduced with additional carbonaceous matter to a point where a commercial grade of slag has been produced through the reduction of iron as Well as tin to metal. iron-tin-alloy known as hardhead thus produced is then generally re-smelted with fresh cassiterite concentrates and through the chemical reaction: `1

the iron in the metal is oxidized by the tin oxide in the fresh charge and returned to slag.

This method of smelting tin concentrates becomes practical when the grade of concentrates is relatively high-say, 50% tin or better-but even at best, requires an expensive rehandling and recycling of slag and hardhead materia/ls.

When the grade of concentrates is loW--say, from or 50% tin down to 10% tin-:this method or reducing tin becomes increasingly impractical as the proportion of the total tin which can be reduced from the slag without reduction of iron with it becomes less and less,

In .order to avoid this diiiiculty, various schemes have been proposed whereby the tin is separated from the iron by makinguse of the fact that stannous sulfide is volatile at elevated temperatures at which iron suliide is not volatile.

i Tin oxide such as cassiterite SnOz may be turned to stannous sulfide by contact with sulfur in suflicient quantities to carry out the reaction:

according to the simplified equation: l

have contemplated and practiced the suldation The.

ci' the original concentrate by a variety of methods such as the passage of a mixture of concentrates, carbonaceous matter and sulfurbearing matter through a heated rotary kiln, and elimination of volatilesulfldes, or by briquetting tin oxide concentrates with coal and sulfur or pyrite, and heating over a coke red grate, or passing through a shaft furnace, etc.

In general` it may be said that the most economical way of reducing tin is by simply smelting the ore with carbonaceous matter either in a reverberatory or shaft type of furnace, but that-as shown above-when the grade of concentrates is too low this simple reduction becomes uneconomical. Also that the suldation to .a volatile stannous sulfide, the oxidation of' stannous sulde to stannic oxide fume, the collection of the fume, and the reduction of this fume to metal, is more expensive per unit of tin than the straight reduction with carbon of tin oxide concentrate to tin metal.

General commercial practice has therefore been to attempt normal smelting of tin with carbonaceous material when the grade of concentrates made it possible, and when the grade 'of concentrates was too low to do this economically the concentrates have been put through one or another of the methods of sulfidation and volatilization of tin. In previous practice, it has only been attempted to sulfidize the tin from the original ore or from other solid tin bearing material and not to sulfldize tin from liquid silicate slags resulting from preliminary carbonaceous reduction of concentrates.

It is an object of the present invention to provide an improved procedure for the recovery of tin, and its separation from other metals or impurities. Another object-is to provide an improved procedure by which tin may be economically separated from relatively low grade ores or concentrates containing relatively large amounts of iron and silicates. A further object is to provide an improved procedure for the fuming of tin in the form of sulfides. Other objects will become apparent.

l It has now been found that it is possible to separate tin from liquid silicate slag containing combined tin silicates by blowing through such a bath of liquid slag a combination of air, fuel oil (or other carbonaceous matter) and iron pyrites or other sulfur-bearing material. The tin com bined as a silicate is partly reduced to metal by th'e reducing action of the flame under the bath and at the same time sulfldized to volatile sulfide by the pyrite introduced with the air and fuel. An apparatus suitable for carrying out this reduction and sulfidization is described in capending patent application Serial No. 349,467, filed August 2,1940, now Patent 2,261,559, issued November 4, 1941. Because of this practical method 'of separating tin from molten slag byvolatilization, it is preferred in the smelting of tin to combine the merits of direct reduction with carbostream of reducing gases and sulfur-bearing material introduced by blowing a combination of air,

. fuel and pyrites or other sulfur-bearing materials under the surface of the liquid bath, as described in more detail hereinafter, in order to separate by volatilization that proportion of the original `tin which cannot be separated from iron because or in a separate furnace.

By this means complete flexibility of tin smelting practice is achieved so that the'same furnace units can treat economically tin concentrates ranging from 9% tin all the way to high grade concentrates running, say, 60% tin or better. If the grade of concentrates is so low that it is not practical to attempt direct reduction to metal in the first smelting, only sufficient reducing agent is added to reduce the stannic and ferric oxides to stannous and ferrous silicates and the Whole melt is then subjected to the sulfdizing and volatilizing blow. In practice, tin concentrates running from 9 up to 18 or 20% tin are treated in this manner. With concentrates running perhaps 25% tin or better, it pays to add sucient carbonaceous matter 1 in the original smelting to form iron free tin metal covered by a layer of high-tin slag which may run from 10 to 15% tin, skim ofi this slag from the metal,

and subject it to the sulfidizing and volatilizing blow. As the amount of tin in the concentrates increases, a larger proportion of the total tin is brought down in the first reduction.

Most Bolivian concentrates contain some iron pyrites Aalong with the tin,l and iron oxides. Where the grade of these concentrates is so low that it scarcely pays to -attempt reduction to metal in the first smeltingoperation, it is preferred to leave these sulfides in the charge to the first smelting furnace where they have the effect of suliidizing some of the tin inthe flrst smelting operation. For example, a 20% tin con-- centrate containing approximately 3% sulfur present as iron pyrite, may be smelted in a reverberatory furnace Withapproximately 8% anthracite coal. The sulfur present in this charge will cause approximately three times its own weight of tin to b'e volatiliaed in this first furnace so that the product of the furnace willbe a tiniron-silicate slag running approximately 14% tin naceous matter with the method of separation by' tallic tin and a molten slag containing whatever proportion of tin is necessary to avoid the reduction of metallic iron with the metallic tin. This fluid, but high-tin slag, is then subjected to a and a tin fume containingapproximately onehalf the tin in the original charge. If the grade of concentrates is, say, over 25% tin and still contains some sulfur, it is preferred to first roast these concentrates for elimination of the sulfur..v

in order to prevent volatilization of tin in the first smelting operation, and bring down as much tin as possible as metal in this operation. 'Ihe exact determination of the point where it pays to roast the concentrates and make tin metal in the first smelting operation depends on the combination of economic factors involved.

In giving aspeciic example of the invention, reference will be made to the treatmentvof a Bolivian cassiterite containing about 20% tin, mostly as stannic oxide (SnOz). together with small amounts of lead, arsenic, antimony, bismuth, silver, zinc, copper, iron, gold, etc., in the form of oxides, suliides or silicates.

l Primary reverberatory The pulverized ore may be mixed with powdered coal (Anthracite Breeze) -in the proportions, for example, of about 6 to 10% coal, based on the weight of ore. In the reverberatory fur-` nace, the mixture is heated to about 2300 to 2500 F. and the ferric iron contained in the mixture is reduced to ferrous iron resulting in a slag containing about 10 to 14% tin, probably in the form of silicates, together with iron and calcium silicates. About 50% of the tin present in the ore may be fumed oif in this operation and caught in a fume separator, such as a bag house or electric precipitation separator. In the treatment of such an ore by the procedure described above, no metal fraction is formed and the molten slag may be conveyed or ilowed to the next treatment in the converter.

Converter In the converter, which may be a horizontal converter having tuyres as described in the above mentioned Patent 2,261,559, iron pyrites, oil and air may be introduced so as to provide a reducing and sulfldizing atmosphere within the molten mass. In this operation the slag from the primary reverberatory may be tapped (without freezing) into theconverter and the dry pulverized pyrites, in the proportions of about of the slag from the first reverberatory furnace, may be introduced by allowing it to fall into a stream of air and thereby. blowing it into the molten slag in the converter, heated to about 2250 to 2500 F., through the said tuyres. oil and additional air may be introduced through other lines communicating with the tuyres, the proportions of total air to oil being such that the oil will burn beneath the surface of the molten slag and keep it hot, but will be insuilicient for complete combustion of the oil and any excess sulfur from the pyrites over and above that required to suldize the .reduced'tin, thus providing a reducing atmosphere and one that tends to reduce the tin oxides of the slag to tin. The added iron pyrites, in addition'to its reducing action, liberates sulfur and permits the suldization of the tin and its volatilization as a tin sulde. The amount of air. may be in excess of that required to completely burn the oil that enters the tuyres but, because of an excess of pyrites carried by.

the gases, may still provide a condition that ls reducing as well as sulfidizing to the tin. As an example of suitable proportions for producing a reducing and sulfidizing atmosphere within the body of the molten slag, about 2'75 to 350 cubic feet of free air per minute is introduced into about 5 tons of molten slag, prepared as described above, together with about 12 to 14 gallons per hour of oil (such as any low viscosity, easily atomized, light fuel oil) and about 500 pounds per hour of iron pyrites. p

The preferred total amount of pyrites to treat a slag as described above is about 1.6 pounds of pyrites per pound of tin content of the slag and the time of 'blowing the converter is regulated by the rate at which the pyrites is i'ed. For example, if a 10,000 pound slag charge c'ontaining 14% or 1400 pounds of tin is added to the converter, about 2240 pounds of pyrites should be blown through the slag. If the pyrites is blown at a rate of 500 pounds per hour, the slag -Will be ilnished in about 4%: hours. If the pyrites is blown at a rate of 400 pounds per hour, the

slag will be ilnished in about 5% hours, etc. The

it is dimcult to reduce the slag to the desired4 limit of less than 0.5% tin. Beginning at about 2300 F., however, the temperature is sufficient to permit complete reduction of thetin t'fonifeni'.

of the slag. The upper limit of 'temperature'. i.'e., around 2500 F., is set by factors of economy, such as the time available, the eifect upon the brick work of the converter, etc.

' This treatment converts the tin to tin sulfide,

which is vaporizedand is immediately burned to tin oxide in the atmosphere above the slag. T'he tin oxide goes oi as a fume and is' caught in the fume separator. Lead, zinc, bismuth, arsenic, antimony and silver, if present in the slag,

1/1 or less of tin) may go to waste.

In this operation the sulfur also may be introduced in other forms, for example, in the form of other sulfur compounds or as free sulfur. However, a marked advantage is obtained by the use of iron pyrites for this purpose. Also, if

desired, the bags in which the ore was received may be baled and charged to the converter to recover the small amount of tin retained by the bag material.

Fume separation The fumes from -the primary reverberatory and from the converter may be collected together in the fume separator, which may be of any suitable type, for example, a bag house and/or electric precipitator.

Secondary reverberatory` The separated fume is chargedinto a secondary reverberatory (which may be the same or a different furnace from the primary reverberatory), together with a carbonaceous material and proper uxes and the necessary amount of water. For example, the fume may be mixed with about 12 to 2.0% powdered coal (anthracite breeze) and suilicent water to pelletize .the mixture. This mixture is then introduced into the secondary reverberatory furnace, together with about 3 to 5% of soda ash, and the mixture is heated to a temperature of about 2000 to 2300 F., the imitation on the low side being the point above which a fluid slag is formed from the mixture of soda ash added to the charge and the ash content of the coal which it fluxes. The upper limit is designated as` 2300 F., since above that temperature there is a very heavy refuming ofthe metal as it is reduced from the fume of the. charge. The mixture of the charge with water is advisable, apparently. because the water reacts with the coal to form hydrogen and carbon monoxide, and these gases are the actual reducing agents which reduce the SnOz of the fume to tin. If the charge is dry, it is necessary to raise the temperature so high that the einciency of reduction becomes very low and a great deal of the tin is simply refumed. Also, it is advisable to carry out this reduction in what is known as a wet furnace. In other words, the charge should be added over a relatively deep bath in the furnace, and in such small-unit quantities that each additional charge will float on this metal bath. 'Ihe presence of a liquid layer on which the reducing charge floats has the effect of collecting the tin pellets as they reduce out of the charge.

In this furnace most of the tin is reduced to metal, along with most of the copper, iron, gold, silver, arsenic, antimony, lead and bismuth present in the fumes. The zinc present in the fumes is refumed in this reverberatory along with minor proportions of the other metals. This zinc-enriched fume can be caught in a separate bag house whenever the zinc has built up a sufficient proportion to warrant its separation from the other metal oxides by leaching or by other conventional means. The residue from the leaching, or other treatment to remove zinc, or the fume Separated if it is not so leached or treated, may be returned to the-second reverberatory furnace.

'Ihe slag from the secondary reverberatory furnace contains a small amount of tin together with traces of other metals and may be returned to the primary reverberatory or to the converter.

Refining operations 'I'he metal fraction from the second rever*- beratory furnace may be tapped off and further rened by the usual methods, such, for example, as sulfur drossing to remove copper, iron and arsenic, aluminum or sodium drossing to remove antimony, stannous chloride drossing to remove lead and if necessary by electrolytic refining, for

example, in a sodium sulfide electrolyte.

In `the specific example given above, reference has been made to the treatment of a Bolivian cassiterite containing about 20% tin, but it is not intended to thereby limit the invention to such an ore and obviously variations in details may be necessary or desirable with tin from other sources. For example, as pointed out above, in treating a tin ore or concentrate containing 25% or more of tintogether with a sulfur content of 3% or more, it may be desirable to pass the pulverized ore or concentrate through a roaster, for example of the Herreshol type, to remove the sulfur before the initial smelting step. If this procedure is followed, the dust may be separated from the roaster gases from the roaster and returned to the cooled roasted ore or concentrate to be smelted. The cooled roasted ore or concentrate may be then subjected to the procedure as described above, suitable variations being made for the diierences in the material being treated.

For example, a larger amount of coal dust may be added in the primary reverberatory to reduce a portion of the tin to metallic tin and the reduced metal fraction may be separated and further treated in the refining operations or may be used to build up the initial liquid metal level in the second reverberatory.

The drawing is a diagrammatic flow sheet illustrating an application of the process, the legends on the drawing indicating the various steps of the operation.

It is obvious that many other variations may be made in the above procedure and it is not intended to limit the inventionto the particular sequence of steps, temperature, pressures, proportions, etc. given in the illustrative example.

'Also, the various steps described may be used alone and with other preparatory steps or with other subsequent steps. For instance, the tin may be separated from the iron and silicates by the primary reverberatory treatment and the converter treatment as described and the fumes separated thereby may be subjected to other treatment to concentrate and rene the tin therein.

Or the blowing of a combustible substance, such asv oil, and a sulfur-containing substance, such as iron pyrites, and an oxygen-containing gas, such as air, in such proportions as to give an incomplete combustion and reduction and sulfldization beneath the surface of the substance to be treated may be applied to other tin-containing substances than the molten slag; for example, it may be applied to the removal of tin from a metal fraction containing reduced tin and iron. Also, the tin-containing substance may be reduced, while avoiding reduction of iron to metal as described herein, and the tin may be volatilized from the slag by other treatments, such, for example, as by blowing chlorine gas, or a chlorinecontaining substance, through the molten slag.

Other agents may be used in place of coal dust to obtain the reducing in the primary or secondary reverberatories or the converter. For example, charcoal, coke, such as petroleum coke, or similar solid carbonaceous reducing materials, or gaseous reducing materials may be used in place of coal dust or in place of each other. Also, other uxing agents may be used in the secondary reverberatory in place of soda ash; for example. calcium fluoride, borax, lime-iron silicate or other low temperature slag forming ingredients Y that will take up slag forming ash from the coal and which will form a slag that will protect the metal of the bath from the oxidizing effect of the reverberatory flame. The ores or concentrates treated usually contain suiicient iron and. silica to form an easy melting slag. If they do not, lime, silica or other slag forming ingredients, such as borax, soda ash, fluorides, etc. may be added. The addition of lime to the ore or concentrate makes it possible to produce a slag containing less tin and thus throw a smaller burden on the converter. Whether or not this would be advisable is a question of economics of operation. Also, iron scrap may be added in this step, if desired, to assist in the subsequent removal of arsenic. 'Ihe various smelting, converting, fume separating, and other steps may also be carried out in other forms of apparatus and it is not intended to restrict the invention to the particular equipment mentioned in the illustrative example.

Various provisions, of course, may be made for economizing heat. For example, the fumes from one or more of the various heating steps may passthrough a heat interchanger, for instance, in a waste heat steam boiler, and the steam may be utilized in subsequent steps, such as to heat the electrolyte in the electrolysis tanks.

The terms used in describing the invention have been used in their descriptive sense and not as terms of limitation and it is intended that all equivalents thereof be included Within the Scope of the appended claims.

What I claim is:

l. In the separation of tin from tin-containing materials containing iron, the steps comprising smelting the material under reducing conditions throughout the mass in the presence of a slag forming material and without the formation of a substantial quantity of matte, said reduction being vsuii'cient to reduce ferric iron to ferrous iron but insufficient to reduce substantial quantities of ferrous iron to metal, separating from any metal fraction the resultant molten slag containing substantially Q11 of the iron and suilicient tin Yto prevent reduction of ferrous iron to metal during the aforesaid reduction and suldizing the molten slag to volatilize tin contained therein.

2. In the separation of tin from tin-containing materials containing iron, the steps ,comprising subjecting the material to a carbonaceous reduction throughout the mass in the presence of a slag forming material to reduce ferric iron to ferrous iron without the formation of a substantial quantity of matte, arresting the reduction before a substantial quantity of ferrous iron is reduced to metal. separating from any resulting metal fraction the resulting molten slag containing substantially all of the iron and suicient tin to prevent reduction of ferrous iron to metal during the aforesaid reduction operation and volatilizlng the tin from the molten slag.

3. In the separation of tin from tin-containing materials containing iron and silicates, the steps comprising hsubjecting the material to a carbonaceous reduction throughout the mass to reduce ferric iron to ferrous iron without the formation of a substantial quantity of matte, arresting the Areduction before a substantial quantity of ferrous iron is reduced to metal, separating from any resulting metal fraction the resulting molten slag containing substantially all of the iron and suicient tin to prevent reducing flame through the molten slag to volatilize tin contained therein.

7. In the separation of tin from tin-contalning materials containing iron, the steps comprising smelting the material under reducing conditions throughout the mass in the presence ofa` slag forming material and without the formation of a substantial quantity of matte, said v substantially all of the iron and suflcienttin duction of ferrous iron to metal during the aforesaid reduction operation and subjecting the molten slag to suldization to volatilize tin contained therein.

4. In the separation of tin from tin-containprevent reduction offerrous iron to metal during the aforesaid reduction from any metal fraction and blowing sulfur-containing material in a reducing atmosphere through the molten slag to volatilize tin oontainedtherein.

5. In the separation of tin fr om tin-containing materials containing iron, the steps comprising smelting the material under reducing conditions throughout the mass in the presence of slag forming materials and without the formation of `a substantial quantity of matte, said reduction being suflcient to reduce ferric iron to ferrous iron but insumcient to reduce substantial quantities of ferrous iron to metal, separa*- ing the resulting molten slag containing substantially all of the iron and sufficient tin to prevent reduction 'of ferrous iron to metal during the aforesaid reduction from any metal fraction and blowing iron pyrites in a reducing atmosphere through the molten slag to volatilize tin contained therein.

6. In theseparation of tin from tin-contain- I ing materials containing iron and silicates, the

to prevent reduction of ferrous iron to metal forming the aioresald reduction from any metal fraction, sulridizing the slag to volatilize tin contained therein, collecting the fume dust from the suldizlng step' and heating it in a reducing atmosphere to reduce the tin to metal.

8. 1n the separation of tin from tin-containing substances containing iron,` the steps of heating the tin-containing substance in the presence of a carbonaceous reducing agent and a slag forming -substance to smelt the mixture under reducing conditions throughout the mass to reduce ferric iron t'o ferrous iron without substantial reduction of the ferrous iron to metal and withsteps comprising smelting the material under reducing conditions throughout the mass and without the formation of a substantial quantity out the formation ofj a substantial quantity of matte, separating any metal fraction and heating the resultant moltenl slag, containing substantially all of the iron and sufilcient tin to prevent reduction of ferrous 'iron to metal during the aforesaid reduction, in a reducing atmosphere in the presence of a sulfur-containing substance, collecting the fume dust from the sulfldizing step, and heating it in a reducing atmosphere to reduce the tin to metal.

9. In the separation of tin from tin-containing materials containing iron and silicates, the steps comprising smelting the material under reducmg conditions throughout the mass and without the formation of a substantial quantity of matte, said reduction being sufficient to reduce ferric iron to ferrous iron but insuflicient to reduce substantial quantities of ferrous iron to metal, separating from any metal fraction the resulting molten slag containing substantially all agents and refining the resultant tin-rich metal.

10. In the separation of tin from tin-containing substances containing iron, the steps of heating the tin-containing substance in a reducing atmosphere throughout the mass in the presence of a slag forming substance to smelt the mixture without the formation of a substantial quantity Y of matte, reduce frric iron to ferrous iron and fume off aportion of the tin without substantialV reduction of .ferrous iron to metal, heating the resultant molten slag, containing substantially all the iron and sufficient tin to prevent reduction of ferrous ir'on to metal during the aforesaid reducing operation, in a reducing atmosphere in the presence of a sulfur-containing substance to fume off more of the tin, collecting the fume from the smelting and sulfldizing operations and heating it 'in a reducing atmosphere to reduce the tin to metal.

1l. In the separation of tin from tin-containing substances containing iron, the steps of heating the tin-containing substance in. a reducing atmosphere throughout the mass in the presence of a slag forming substance to smelt the mixture without the formation of a substantial quantity of matte, reduce ferrie iron to ferrous iron and fume off a portion of the tin without substantial reduction of ferrous iron to metal, heating the resultant molten slag, containing substantially all the iron and suicient tin to prevent reduction of ferrous iron to metal during the aforesaid reducing operation, in -a reducing atmosphere in the presence of iron pyrites to fume off substantially all of the remainder of the tin, collecting the fume from the smelting and suldizing operations and heating it in a reducing atmosphere in the presence of a iluxing agent.

12. In the separation of tin from tin-containing substances containing iron, the steps of heating the tin containing substance in the presence of coal dust to smelt the mixture under reducing conditions throughout the mass to reduce ferric iron to ferrous iron without the formation of a substantial quantity of matte and fume off a portion of the tin without substantial reduction of ferrous iron to metal, separating any metal fraction and heating the resultant molten slag, containing substantially all of the iron and su'iiicient tin to prevent reduction of ferrous iron to metal during the aforesaid reduction, in a reducing atmosphere in the presence of iron pyrites to fume off substantially all of the remainder of the tin, collecting the fume from the smelting and suldizing operations and heating it in the presence of coal and soda ash to reduce the tin to metal.

13. In the separation of tin from tin-containing substances, the steps of blowing through the ing substance and provide a reducing and sul- Ilidizing atmosphere beneath the surface of the molten slag.

15. In the separation of tin from tin-containing substances, the steps of blowing through the molten substance, oil, air, and iron pyrites in proportions to cause an incomplete combustion and a reducing and suldizing atmosphere beneath the surface of the molten material.

16. In the separation of tin from tin and iron containing substances, the steps of heating the substance in a reducing atmosphere throughout the mass in the presence of a. slag' forming substance to smelt the mixture without the formation of a substantial quantity of matte, reduce ferric iron to ferrous iron and fume on a portion of the tin, heating the resultant *molten slag, containing substantially all of the iron and suicient tin to prevent reduction of ferrous iron to metal during the aforesaid reduction, in a reducing atmosphere in the presence of a sulfur bearing substance to fume olf more of the tin, collecting the fume from the smelting and suldizing operations, heating it in a reducing atmosphere to reduce tin to metal, and separating and further refining the metal fraction.

17. In the separation of tin from tin and iron containing substances, the steps of heating the substance in a reducing atmosphere throughout the mass in the presence of a slag forming substance to smelt the mixture without the formation of a substantial quantity of matte, reduce ferric iron to ferrous iron and fume off a portion of the tin, blowing throughvthe molten slag, containing substantially all of the iron and sufficient tin to prevent reduction of ferrous iron to metal during the aforesaid reduction, a carbonaceous combustible substance, an oxygen containing gas, and a sulfur-containing substance, in ,proportions to cause an incomplete combustion of the carbonaceous and sulfurcontaining substances and provide a reducing and suliidizing atmosphere beneath the surface of the molten slag.

18. In the separation of tin from a tin ore or concentrate containing iron and over about 20% tin and a sulfur bearing material, the steps of roasting ,the material to remove sulfur, returning the dust to the roasted material, heating theroasted material in a reducing atmosphere throughout the mass to reduce tin to metal and ferric iron to ferrous iron but with insufficient reduction to reduce ferrous iron to metal, separating the metal fraction, heating the resultant molten slag, containing substantially all of the iron and sufcient tin to prevent reduction of ferrous iron to metal during the aforesaid reduction, in a reducing atmosphere in the pres ence of a sulfur bearing substance to fume off tin, collecting the fumes from the reducing and V suliidizing steps and heating it in a' reducing atmosphere to reduce tin to metal.

19. In the separation of tin from a tin ore or concentrate containing iron and not over about 25% tin, the steps comprising heating the material in a reducing atmosphere throughout the mass and without the formation of a substantial quantity of matte, said reduction being suicient to reduce ferric iron to ferrous iron but insufficient to producev a metal fraction, heating the resultant molten slag, containing substantially all of the iron and suiiicient tin to prevent reduction of ferrous iron to metal during the -aforesaid reduction, in a reducing atmosphere in the presence of a sulfur bearing substance to fume off tin, collecting the fumes from the reducing and suli'ldizing steps and heating it in a reducing atmosphere to reduce tin to metal.

WILLIAM H. OSBORN.

' CERTIFICATE or CORRECTION. Pstent No'. 250149197. December 8, 19,42.

WILLIAM II. osBoRN'.

It 1s hereby certified that error appearsl In vthe printed specification-- of the above numbered patent requiring correction as follows: Page 5 firstv column, lines )4.2 and 11.5', glam 1+, 1ines58 and 59;,claim 5, and second column,

lines l5Y and 16, claim 7, strike -out from anymetal fraction"v and insert the same before 'the resulting" in first column, lines'l59 and 55A, and

second column, lifne l2, claims li, 5 and 7 .respectiVr-ly;` and'page-., second column, line l5, for forming read during-; and that the smid Letters Patent should'hbe read with this correctionrtherein that the same may conform to record of the case 'in the' Patent Office. I

signed and sealed thiszh day'of January,A. D; 19H5.

Henry Van vArsdale,

(Seel) Acting ommissioner of Patents. 

